Metal filling method and memeber with filled metal sections

ABSTRACT

In the formation of through wirings in a silicon substrate and so forth, there was a need for the development of a technology that would allow metal to be reliably filled particularly in the vicinity of openings of through holes and other fine holes. This invention provides a metal filling method and member with filled metal sections in which, in the inflow and filling of a plating solution into through holes  11  of a substrate  10  by immersing said substrate  10  in heated and melted conductive metal, filled metal sections are formed by preliminarily forming a metal layer  15  on the inner surface of one of the ends of through holes  11  of this substrate  10  as well as on substrate top surface  13  around those openings, removing substrate  10  on which inflow and filling of the plating solution into through holes  11  has been completed from the plating solution, and then cooling to solidify the plating solution that has been filled into the through holes.

BACKGROUND ART

[0001] The present invention relates to a metal filling method andmember with filled metal sections in which a metal is filled into fineholes formed in a member, such as through holes or non-through holesformed in a circuit substrate.

[0002] For example, in the case of forming through hole electrodes (viahole electrodes) in a substrate (such as a silicon substrate) in theproduction process of an IC chip and so forth, a plating method istypically used in which through holes for the through hole electrodesare opened in the substrate, the substrate is inserted into a platingsolution (molten metal) in which a conductive metal has been solved, andimmersed in that the plating solution to fill the into the conductivemetal through holes.

[0003] However, in the case of filling metal into through holes by theplating method, there are cases in which, for some reason, the platinglayer concentrically grow near the through hole entrance of thesubstrate, thereby making it difficult for plating liquid to enter tothe back of the through holes. In this case, there are problems such asthe occurrence of roughness within the through holes that made itdifficult to fill metal in a state free of voids.

[0004] In cases in which the through holes are fine holes having a highaspect ratio (depth of the hole/opening diameter of the hole) inparticular, since it is difficult for the plating solution to penetrateto the back of the through holes, concentrated growth of the platinglayer near the through hole entrance of the substrate occurs easily,causing the problems described above to become remarkable. For example,in the case of high-density, three-dimensional mounting consisting ofthe stacking of silicon IC chips and so forth, although there are casesin which through electrodes (through wirings) are formed in thesubstrate for connecting the wiring patterns on the top and bottom of asubstrate, since the through holes for through electrodes opened in thesubstrate are fine holes having a high aspect ratio, if throughelectrodes are attempted to be formed by filling metal into the throughholes using the plating method described above, it is difficult toreliably form through electrodes that are free of voids.

SUMMARY OF THE INVENTION

[0005] In consideration of the above problems, the object of the presentinvention is to provide a metal filling method and member with filledmetal sections that allows filling of a plating solution to be carriedout reliably particularly near openings that open on the outer surfaceof a work piece of fine holes formed in that work piece.

[0006] The metal filling method according to the present invention is amethod for filling metal into fine holes formed in a work piece, and ischaracterized by forming a metal layer on the inner surface of an end ofeach fine hole that opens in an outer surface of the work piece,followed by immersing the work piece in the plating solution, fillingthe plating solution into the fine holes, removing the work piece fromthe plating solution with one of ends along an axial direction of eachfine hole still occluded, and then cooling the work piece.

[0007] In this metal filling method, a constitution can also be employedin which the fine holes are through holes that pass through the workpiece, the metal layer is formed on the inner surface of at least oneend of both ends in the axial direction of each through hole, and whenthe work piece, which has been immersed in the plating solution to fillthe plating solution into the through holes, is removed from the platingsolution, an opening in the other end of the axial direction of eachthrough holes is occluded with a sealing material as the above one ofends along the axial direction of each fine hole. Moreover, the metallayer can be formed on the inner surface of the end of the fine holethat opens in the outer surface of the work piece as well as on theouter surface of the work piece extending around the end of the finehole on which the metal layer is formed. In this case, after immersingthis work piece in the plating solution within a plating solution bathto fill the plating solution into the fine hole but prior to cooling ofthe work piece, the plating solution filled into the fine hole is paddedat the sites where the metal layer was formed on the inner surface ofthe end of the fine hole that opens on the outer surface of the workpiece and on the outer surface of the work piece extending around theend of the fine hole on the work piece which is removed from the platingsolution. And then, a filled metal section formed by solidification ofthe plating solution within the fine holes, and an external metalsection formed by solidification of the padded sections of the platingsolution, are formed unitarily by cooling said work piece.

[0008] In addition, in the metal filling method as claimed in thepresent invention, the metal layer around the openings of fine holes inthe outer surface of a work piece can also be patterned corresponding tothe shape of the external metal sections to be formed prior to immersingthe work piece in the plating solution.

[0009] The member with filled metal sections according to the presentinvention is a member with filled metal sections having filled metalsections formed by filling a metal into fine holes formed in a workpiece, and is characterized by a metal layer being formed on the innersurface of an end of the above fine holes that opens to the outersurface of the work piece, and the filled metal sections being filled ata site that includes the end of the fine holes on which the above metallayer is formed. A constitution can also be employed for this memberwith filled metal sections in which a metal layer is formed not only onthe inner surface of the end of the fine holes that opens in the outersurface of the work piece, but also on the outer surface of the workpiece that extends around the end of the fine holes on which the metallayer is formed, and external metal sections, which are unitarily formedwith the filled metal sections, and padded so as to protrude from theouter surface of the work piece, are formed so as to cover the metallayer.

[0010] The work piece as claimed in this invention is a member havingfine holes for metal filling that are either through holes (fine holes)or non-through holes (fine holes in which only one end in the axialdirection open on the outer surface of the work piece, while the otherend are not open), examples of which include a substrate (circuitsubstrate) in which via holes or so-called inner via holes are formed.In addition to semiconductor materials such as silicon or galliumarsenide (GaAs), various other materials such as glass or otherinsulating material can be used for the material of the work piece.

[0011] Examples of methods for forming fine holes (through holes ornon-through holes) in the work piece as claimed in the present inventioninclude Deep-Reactive Etching (DRIE) as is represented by InductivelyCoupled Plasma-Reactive Ion Etching (ICP-RIE), wet etching methods usingan etching solution, mechanical processing methods using a microdrill,and optical excitation electrolytic polishing. Fine hole diameter, workpiece dimensions, fine hole depth-and so forth are suitably setaccording to the application and so forth, and the cross-sectional shapeof the fine holes (shape of the cross-section perpendicular to the axialdirection) may be of any shape such as circular, oval, triangular orrectangular (including a square).

[0012] In the metal filling method as claimed in the present invention,a technique is employed in which, after immersing a work piece in aplating solution which is composed of heated and melted conductive metaland filling this plating solution into the fine holes by allowing aplating solution to flow into the fine holes, the work piece is removedfrom the plating solution with one of the ends in the axial direction ofthe above fine holes still occluded, after which the work piece iscooled to solidify the plating solution in the fine holes. In the casethe fine holes are through holes, through wirings and so forth can beformed by solidifying the plating solution that has been filled into thefine holes of the work piece, and in the case the fine holes arenon-through holes, internal electrodes, internal wirings and so forthcan be formed in the form of filled metal sections by the solidifiedconductive metal.

[0013] Furthermore, when removing the work piece from the platingsolution, having one of the ends in the axial direction of the fineholes still occluded can be realized by covering one of the ends alongthe axial direction of each through hole using a sealing material in thecase the fine holes are through holes. In addition, in the case the fineholes are non-through holes, since the constitution of the non-throughhole itself is such that one end along the axial direction is open whilethe other end is blocked, it goes without saying that the use of asealing material is not required.

[0014] In the metal filling method as claimed in the present invention,since the heated and melted conductive metal is filled into fine holes,defective filling caused by concentrated growth of the plating layer atthe entrance of fine holes in the case of a plating method (includingthe formation of voids as previously described) can be avoided. In thepresent invention, “plating solution” refers to this heated and meltedconductive metal.

[0015] In the present invention, immersion of the work piece into theplating solution refers to submerging the work piece in the platingsolution, or in other words, the work piece is inserted into the platingsolution. However, the immersion referred to here is not limited to theimmersion of the work piece into the plating solution stored in a bath(to also be referred to as a plating solution bath), but also includesthe injection of the plating solution into a container that houses thework piece (including the above plating solution bath). Here, “filling”into fine holes is not limited to filling entire fine pores withoutvoids, and a constitution in which, for example, voids are left in aportion of the fine holes in the axial direction (case of filling metalinto inner via holes or other non-through holes) or a slight amount ofspace is present in the filled metal, is also included. In the presentinvention, as a result of being able to reliably fill metal near theentrance of the openings of the fine holes in particular, the electricaland mechanical properties of the filled metal sections can be adequatelysecured. In addition, “removal” of the work piece from the platingsolution includes lifting up the work piece from out of the platingsolution retained in a bath, removing the work piece in the horizontaldirection, and exposing a work piece that has been immersed in theplating solution in a bath by discharging the plating solution frominside the bath.

[0016] However, as a result of the inventors of the present inventionverifying the filled status of the plating solution within fine holesafter removing a work piece in the form of a substrate formed fromsilicon and glass from the plating solution, merely a method is used inwhich a work piece in which the plating solution has flown into andfilled fine holes is simply lifted out (equivalent to “removed”) fromthe plating solution with the closed side among both ends in the axialdirection of each fine hole is the lower end, it was found that, as aresult of it being easy for the plating solution to flow out from theopening of each fine holes that opens on the upper surface duringremoval of the work piece, and the plating solution flowing out duringremoval, there are many cases in which there is insufficient filling ofthe plating solution during cooling and solidification: Since the amountof the plating solution contained in the fine holes decreases if outflowof the plating solution occurs, as shown in FIG. 15, for example, theupper surface of the plating solution 2 within each fine hole 1 (throughholes are shown in FIG. 15) ends up being slightly lower than the uppersurface 4 of work piece 3 (a substrate in FIG. 15), resulting in theformation of level difference D. In addition, if this level differenceis formed as shown in FIG. 15, even if, for example, bumps are attemptedto be formed and bonded in a separate step on through wirings in whichthe plating solution has solidified, there is susceptibility to theoccurrence of bonding defects between the bumps and through wirings,which can easily become a cause of defects such as incomplete electricalconnections.

[0017] The phenomenon in which the plating solution flows out from thefine holes during removal of the work piece from the plating solution iscaused by being unable to ensure adequate wettability with the platingsolution in the case of using silicon and glass to form the work piece.That is, since there is a lack of acclimation between the inner surfacesof the fine holes and the plating solution, outflow of the platingsolution from the fine holes occurs easily.

[0018] In the present invention, wettability with the plating solutionthat has been filled into fine holes is ensured by a metal layer formedon the inner surface of the end of each fine hole that is an upper endwhen the work piece is removed (by being lifted out and so forth) fromthe plating solution. As a result, when the work piece is removed fromthe plating solution, it is difficult for the plating solution to flowout from the openings of the fine holes, thereby being able to preventproblems such as the formation of a level difference near the openingsof the fine holes. The metal layer is preferably formed over as a broadrange as possible on the inner surface near the entrance of each finehole. In the case the fine holes are through holes, if a metal layer isformed on the inner surface of both ends of each through hole, even ifthe metal layer is not formed over the entire inner surface along thelengthwise direction in the axial direction of the through hole, theplating solution is effectively acclimated throughout the entire throughhole, thereby being effective in preventing the formation of voids andso forth within the through hole.

[0019] If a metal layer is formed on the inner surface of the end ofeach fine hole that opens to the outer surface of the work piece, aswell as on the outer surface of the work piece that extends around theend of the fine hole, the outflow of the plating solution from the fineholes when the substrate is removed from the plating solution can bemore reliably prevented due to the wettability of the plating solutionwith respect to the metal layer surrounding the openings. In addition,when the work piece is removed from the plating solution, by takingadvantage of the formation of a layer of the conductive metal along thismetal layer (metal layer around the openings), grounded sections, bumpsand other external metal sections of the wiring can be formed on thesubstrate by cooling and solidifying the plating solution on this metallayer. Here, grounded sections, bumps and other external metal sectionsthat are formed refer to those for which the plating solution is cooledand solidified after having been padded at those sites where the metallayer formed around the openings of the fine hole is present, and areunitarily formed with the filled metal sections that are solidifiedwithin the fine hole. Since the grounded sections, bumps and otherexternal metal sections that are formed are continuous with the filledmetal sections by the same type of metal as the filled metal sections,in comparison with the case of forming separately from the filled metalsections, there is the advantage of the absence of problems such asdefective bonding with the filled metal sections. In addition, there arealso no problems such as brittleness of the bonded sections (bondedsections between external metal sections and filled metal sections)caused by differences in the coefficients of thermal expansion ordiffusion of materials and so forth that occur in the case the externalmetal sections and filled metal sections are of different types ofmaterials.

[0020] For example, in the case of forming external metal sections inthe form of bumps on the work piece in the form of the substrate, thesize, shape and so forth can be adjusted according to the range offormation and so forth of the metal layer around the opening of eachfine hole on one side of the substrate. When the substrate is removedfrom the plating solution, since the plating solution that remains atthe sites where the metal layer is present that is formed at the openingof each fine hole and around the openings on one side of the substratecan be padded in a peak-shape due to its surface tension and so forth, apeak-shaped bump can be obtained by solidifying the plating solution.Thus, the height, size and so forth of bumps can be adjusted byadjusting the formation range of the metal layer around the openings offine holes on one side of the substrate by patterning or other means.

[0021] In the member with filled metal sections as claimed in thepresent invention, since superior adherence is ensured between a metallayer and a filled metal section which is filled into the end of eachfine hole on which a metal layer is formed due to the wettability of themetal layer formed on the inside of the end of fine hole that opens tothe outer surface of the work piece, the fixed state of the filled metalsection near the end of the fine hole can be maintained with stabilityover a long period of time, and since peeling of the filled metalsection from the inner surface of the fine hole and lifting of thefilled metal section within the fine hole can be reliably prevented,long-term stability is obtained.

[0022] Moreover, in a constitution in which an external metal sectionunitarily formed with the above filled metal section and padded so as toprotrude beyond the outer surface of the work piece is formed so as tocover the metal layer which is formed on the outer surface of the workpiece and extends around the end of the fine hole on which the metallayer is formed, since the filled metal section within the fine hole andthe external metal section can be formed unitarily, there is nooccurrence of problems such as defective bonding due to bonding ofdifferent types of metals or brittleness of bonded sections caused bydifference in the coefficients of thermal expansion, diffusion ofmaterials, etc.

[0023] According to the present invention, wettability with the platingsolution filled into fine holes is ensured by the metal layer formed onthe inner surface of the end that opens to the outer surface of a workpiece among both ends of each fine hole. As a result, when a substrateis removed from the plating solution, it is difficult for the platingsolution to flow out from the opening of the fine hole, and problems canbe prevented such as the formation of a level difference near theopening of the fine hole. If this level difference is eliminated,bonding can be carried out reliably in the case of bonding bumps and soforth formed in a separate step to filled metal sections of throughwirings and so forth in which this plating solution has solidified,thereby allowing bonding defects to be prevented. In addition, if ametal layer is formed on the inner surface of the end of the fine holethat opens to the outer surface of a work piece, the formation of voidsinside the fine hole (and especially voids that form easily near theoccluded end when the work piece is immersed in the plating solution)can be effectively prevented, thereby enabling the plating solution tobe reliably filled throughout the fine hole and allowing the formationof reliable through wirings free of level differences and voids.

[0024] As a result of forming the metal layer on the inner surface nearthe opening of each fine hole and around the opening of the fine hole onthe outer surface of the work piece, the outflow of the plating solutionfrom the fine hole when the work piece is removed from the platingsolution can be more reliably prevented due to the wettability of theplating solution with respect to the metal layer around the opening. Inaddition, when a substrate is removed from the plating solution, bytaking advantage of the formation of a layer of the conductive metalalong this metal layer (metal layer around the opening), wiring groundedsections, bumps and so forth can be formed on the substrate by coolingand solidifying the plating solution on this metal layer.

[0025] If the above external metal section is formed by cooling andsolidifying the plating solution that is continuous with the fine holeand has been padded at those locations where the metal layer is presentthat has been formed in the opening of each fine hole in the outersurface of the work piece as well as around the opening, since thisexternal metal section is formed unitarily with filled metal sectionformed by the plating solution that solidifies within the fine hole,there is the advantage of the absence of defective bonding and so forthwith the filled metal section. In addition, there are also no problemssuch as brittleness of a bonded section (bonded section between theexternal metal section and filled metal section) caused by differencesin coefficients of thermal expansion or diffusion of materials likethose which occur in the case of the external metal section and filledmetal section being of different materials, thereby resulting inimproved long-term reliability.

[0026] In the formation of the metal layer around the opening of eachfine hole in the outer surface of the work piece, bumps and so forth ofa target size can be formed easily by patterning the metal layeraccording to the target shape of the external metal portions (such asbumps) to be formed. In this case, the range of formation of the metallayer around the opening of the fine hole in outer surface of the workpiece can be adjusted by patterning, offering the advantage of beingable to easily adjust the height, size and so forth of the bumps.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a cross-sectional view of a first embodiment of thepresent invention showing the substrate to be used.

[0028]FIG. 2 is a cross-sectional view showing the state in which anoxide film has been formed as an electrical insulating layer by thermaloxidation treatment of the substrate of FIG. 1.

[0029]FIG. 3 is a cross-sectional view showing the state in which ametal layer has been formed on the substrate following the thermaloxidation treatment of FIG. 2.

[0030]FIG. 4 is a cross-sectional view showing the details of the metallayer of FIG. 3.

[0031]FIG. 5 is a cross-sectional view showing the state in which aphotosensitive resist has been applied to the substrate on which themetal layer of FIG. 3 has been-formed.

[0032]FIG. 6 is a cross-sectional view showing the state in which thephotosensitive resist has been removed from the substrate of FIG. 5.

[0033]FIG. 7 is a perspective view showing an example of forming bypatterning a metal layer on a substrate surface.

[0034]FIG. 8 is a drawing showing the state in which the openings ofthrough holes have been covered by affixing a heat-resistant film to thebottom surface of a substrate on which the patterning of the metal layerof FIG. 7 has been completed.

[0035]FIG. 9 is a cross-sectional view showing a decompression chamberthat is applied to the forming method of through wirings as claimed inthe present invention.

[0036]FIG. 10 is a drawing showing the state in which a substrate hasbeen immersed in a plating solution stored in a plating solution bathinstalled within the decompression chamber of FIG. 9.

[0037]FIG. 11A is a cross-sectional view showing the state in which asubstrate has been immersed in the plating solution after having reducedthe pressure in a decompression chamber, while FIG. 11 B is across-sectional view showing the state in which the plating solution hasbeen filled into through holes of a substrate by pressurizing the insideof the decompression chamber.

[0038]FIG. 12 is a cross-sectional view showing the details of the stateof FIG. 11B.

[0039]FIG. 13 is a drawing showing the state in which a substrate hasbeen removed from the plating solution stored in a plating solution tankinstalled within the decompression chamber of FIG. 9.

[0040]FIG. 14 is a cross-sectional view showing the state in whichthrough wirings and bumps have been formed by cooling a substrate thathas been removed from the plating solution.

[0041]FIG. 15 is a cross-sectional view showing the state in whichthrough wirings have been formed in through holes of a substrate by athrough wiring forming method of a comparative example.

[0042]FIG. 16 is a cross-sectional view showing a substrate that isapplied to a second embodiment of the present invention.

[0043]FIG. 17 is a cross-sectional view showing the state in which ametallization step has been completed on the substrate of FIG. 16.

[0044]FIG. 18 is a drawing showing the state in which the substrate ofFIG. 16 has been immersed in the plating solution in a metal fillingstep following completion of the metallization step, and shows the statein which it has been immersed in the plating solution in a platingsolution bath installed within a decompression chamber.

[0045]FIG. 19 is a cross-sectional view showing the state in whichfilled metal sections and external metal sections have been formed bycompleting cooling of a substrate removed from the plating solution in acooling and solidification step following completion of the metalfilling step of FIG. 18.

[0046]FIG. 20 is a cross-sectional view showing the state in whichfilled metal sections within fine holes have been exposed by polishingthe bottom surface of a substrate in a filled metal section exposurestep following completion of the cooling and solidification step of FIG.19.

[0047]FIG. 21 is a cross-sectional view of a third embodiment of thepresent invention showing an example of having formed filled metalsections and external metal sections according to the metal fillingmethod as claimed in the present invention in a rod-shaped membercontaining a through hole.

[0048]FIG. 22 is a drawing of a step in which the plating solution isfilled into the through hole of the rod-shaped member of FIG. 21 thatshows the state in which a substrate has been removed from the platingsolution stored in a plating solution bath installed inside adecompression chamber.

[0049]FIG. 23 is a cross-sectional view of a fourth embodiment of thepresent invention that shows an example of having formed filled metalsections and external metal sections according to the metal fillingmethod as claimed in the present invention in a rod-shaped membercontaining a non-through hole.

PREFERRED EMBODIMENTS

[0050] The following provides an explanation of embodiments of thepresent invention with reference to the drawings.

First Embodiment

[0051] First, an explanation is provided of a metal filling method andmember with filled metal sections of a first embodiment as claimed inthe present invention.

[0052] The metal filling method of this embodiment is a method forforming through wirings and bumps for connecting wiring patterns on thetop and bottom sides (both the top and bottom sides correspond to theouter surfaces of a work piece) of a work piece in the form of asubstrate (work piece may hereinafter be referred to as the “substrate”,and hereinafter, the metal filling method of this embodiment may bereferred to as the “through wiring forming method”).

[0053] As shown in FIG. 1, the substrate 10 used in this metal fillingmethod has a plurality of fine holes in the form of through holes 11 forthrough wirings (hereinafter, fine holes may be referred to as “throughholes”) formed therein. Here, although a silicon substrate in the formof the substrate 10 is used, the substrate is not limited to this type,but rather semiconductor materials such as gallium arsenide (GaAs),insulating materials such as glass or ceramics, or synthetic resinsubstrates can also be used. Moreover, a compound substrate can also beused in which, for example, an epoxy resin or other organic material isunitarily laminated with a glass or silicon substrate. In addition, asubstrate in which an electrical circuit is formed directly on one orboth primary sides (top and bottom sides), a substrate in which aplatform for forming a circuit is formed on one or both primary sides,substrates that are combinations of these or substrates of various otherconstitutions can also be employed. Furthermore, the thickness of thesubstrate 10 is on the order of several hundred micrometers.

[0054] The through wirings formed in the substrate 10 are equivalent tothe filled metal sections as claimed in the present invention, whilebumps are equivalent to the external metal sections as claimed in thepresent invention. In this embodiment, “substrate” can be read to mean awork piece, “through holes” can be read to mean fine holes, “throughwirings” can be read to mean filled metal sections, and “bumps” can beread to mean external metal sections. In addition, those locations wherea “through wiring forming method” is described can be read to mean ametal filling method.

[0055] This through wiring forming method is composed of a step in whicha metal layer is formed (metallized) on the inner surface of theopenings and around the openings of through holes on the top and bottomsides of a substrate (metallization step), a plating solution fillingstep in which a substrate on which this metallization step has beencompleted is immersed in a plating solution (the conductive metal heatedto melting) stored in a plating solution bath to fill the platingsolution into through holes, and a cooling and solidification step inwhich through wirings and bumps are formed by solidifying the platingsolution within the through holes and the plating solution padded in aprotruding state on the substrate continuous with the through holes bycooling the substrate that has been removed (referring specifically hereto being lifted up) from the plating solution bath after the platingsolution filling step.

[0056] (Metallization Step)

[0057] As shown in FIG. 1, the substrate 10 is prepared and an oxidefilm in the form of an electrical insulating layer 12 (hereinafter, anelectrical insulating layer may be referred to as an “oxide film”) isformed on the entirety of the substrate 10 by thermal oxidationtreatment of this substrate 10 (FIG. 2).

[0058] The through holes 11 are fine holes having a diameter on theorder of several tens of micrometers (e.g., 50 μm) that pass through thesubstrate 10, and are opened in a top surface 13 and bottom surface 14of the substrate 10. The oxide film 12 formed by thermal oxidationtreatment of the substrate 10 is formed not only on the top surface 13and bottom surface 14 of the substrate 10, but also on the inner surfaceof the through holes 11.

[0059] Furthermore, here “top surface” refers to surface facing upwardin the plating solution filling step (see FIGS. 9 through 13) to bedescribed later (one side), while the “bottom surface” refers to thesurface facing downward (other side).

[0060] In this embodiment, an explanation is provided of the example ofthe case of using DRIE as the means for forming fine holes (throughholes 11) in a work piece (substrate 10). In the DRIE method of thisembodiment, as a result of using sulfur hexafluoride (SF₆) for theetching gas, and alternately carrying out etching by high-density plasmaand passivation deposition onto the substrate wall surface (Boschprocess), the through holes 11 that pass through the primary surfaces(top surface 13 and bottom surface 14) on both sides of the substrate 10are formed by deep etching of the substrate 10.

[0061] In addition, it goes without saying that wet etching using thepreviously described etching solution or a mechanical processing methodusing a microdrill and so forth can also be employed as the techniquefor forming fine holes (through holes 11) in the work piece (substrate10) besides the above DRIE method. In the case of applying wet etchingto the formation of fine holes in the substrate 10 made of silicone,aqueous potassium hydroxide solution (KOH) and so forth is used for theetching solution.

[0062] Next, as shown in FIG. 3, a metal layer 15 is formed by metalsputtering on the inner surface of the openings (inner surface ofthrough holes in the vicinity of openings) of the through holes 11 onthe top surface 13 and bottom surface 14 of the substrate 10, and aroundthe openings of the through holes 11 on the top surface 13 and bottomsurface 14.

[0063] More specifically, as shown in FIG. 4, a first layer 15 a in theform of a chromium (Cr) layer having a thickness of about 300 Å is firstformed by sputtering, after which a second layer 15 b in the form of agold (Au) layer having a thickness of about 5000 Å is layered and formedon the above first layer 15 a. The metal layer. 15 formed on the innersurface of the through holes 11 is formed at least about several tens ofmicrometers in towards the center in the axial direction of the throughholes 11 from the top surface 13 or bottom surface 14 of the substrate10.

[0064] Furthermore, the metal film 15 may be formed over the entireinner surface of the through holes 11, and in order to reliably fill theplating solution without causing the occurrence of voids inside thethrough holes 11 by ensuring wettability with the-plating solutionfilled in the through holes 11, the metal layer 15 is preferably formedover a wide a range as possible within the through holes 11. In otherwords, the range of which the metal layer 15 is formed on the innersurface of the through holes 11 is at least the inner surface of thethrough holes 11 near the openings of the through holes 11 on the sideof the top surface 13 (a range of at least several tens of micrometersfrom the openings of the through holes 11 towards the center in theaxial direction), more preferably the inner surface in the vicinity ofthe openings in both the top and bottom surfaces of the substrate 10 (inother words, near both ends in the axial direction of the through holes11; and, over a range on the order of at least several tens ofmicrometers from the openings of the through holes 11 towards the centerin the axial direction on either end), and most preferably the entireinner surface of the through holes 11.

[0065] In addition, in the formation of the metal layer 15 usingsputtering, since the metal layer 15 can be formed as long as it isformed within the range that can be reached by metal atoms as a resultof sputtering, other metals may also be used in addition to the chromiumand gold mentioned above.

[0066] On the other hand, the metal layer 15 formed around the openingsof the through holes 11 in the top surface 13 and bottom surface 14 areformed over a larger area than the formation range of bumpscorresponding to the size of the target bumps to be formed (and may beformed entirely over the top surface 13 or top surface 14 of thesubstrate 10), and is patterned to size corresponding to the bumpformation range in the step shown in FIGS. 5 and 6 to be describedlater.

[0067] Furthermore, the metal that forms the first layer 15 a and secondlayer 15 b of the metal layer 15 is not limited to the above-mentionedchromium or gold, but may also be another metal.

[0068] Once formation of the metal layer 15 has been completed, as shownin FIG. 5, a photosensitive resist 16 is applied to the top surface 13and bottom surface 14 of the substrate 10, and this photosensitiveresist 16 is patterned by photolithography technology. Next, as shown inFIG. 6, a metal pattern (made of the metal layer 15) is formed of ashape that matches a desired bump size to be formed around the openingsof the through holes 11 on the top surface 13 and bottom surface 14 ofthe substrate 10 by etching the metal layer 15 (first layer 15 a andsecond layer 15 b). FIG. 7 shows an example of the form of the metallayer 15 formed by patterning. As a result, the metal layer 15 of atarget shape is formed around the openings of the through holes 11 onthe top surface 13 and bottom surface 14 of the substrate 10 to completethe metallization step.

[0069] Furthermore, the formation of the metal layer 15 by patterning onthe top surface 13 and bottom surface 14 of the substrate 10 is notlimited to matching a bump size to be formed, but rather may also, forexample, be formed to a shape that matches the grounding section ofpattern wiring formed on the top surface 13 and bottom surface 14, ormay be formed to a shape that forms a portion of pattern wiring.

[0070] The work piece (substrate 10) in which fine holes are formed issubjected to a plasma pretreatment step prior to filling of the platingsolution. Here, this plasma pretreatment step consists of cleaning for 1minute with oxygen (O₂) plasma to clean and remove plasma layer residueand foreign objects on the outer surface of the work piece with plasma.Consequently, it becomes easy to uniformly fill the plating solutioninto the fine holes. Furthermore, the plasma used for cleaning is notlimited to oxygen plasma, but rather may also be hydrogen (H₂) plasma orargon (Ar) plasma or any combination thereof. In addition, this plasmapretreatment step may not only be carried out prior to filling of theplating solution, but may also be carried out prior to forming the metallayer on the work piece.

[0071] (Plating Solution Filling Step)

[0072] Following completion of the metallization step, as shown in FIG.8, a heat-resistant film in the form of sealing material 17(hereinafter, this sealing material may be referred to as a“heat-resistant film”) is affixed to the bottom surface 14 of thesubstrate 10, to occlude the openings of the through holes 11 on thebottom surface 14.

[0073] Polyimide film, for example, can be used for the heat-resistantfilm, and a particularly preferable example of a polyimide film isKapton (registered trademark). In the case of Kapton, it is preferableto use a grade that does not become hard at the temperature (meltingpoint) of the conductive metal, and in this case, is advantageous withrespect to being able to easily separate the heat-resistant film fromthe substrate 10 after having been removed (more specifically, liftedout; see FIG. 13) from the plating solution 20 in the cooling andsolidification step to be described later. In addition, a compound filmor tape and so forth in which two Kapton polyimide films or differentresin films are laminated using a silicon-based adhesive can be employedfor the heat-resistant film. The use of a sealing material in the formof a film or tape using Kapton (including film composed of Kaptonalone), on one side of which is coated a pressure-sensitive adhesive foradhering to a work piece, is preferable in terms of ease of through holesealing work. However, the above pressure-sensitive adhesive that isused should not become hard at the temperature (meting point) of theconductive metal, and should facilitate peeling from the work pieceafter having been removed from the plating solution.

[0074] It goes without saying that the air pressure in the through holes11 should be at atmospheric pressure when one end in the axial directionof each through holes 11 is occluded by affixing the sealing material17, since the work of affixing the sealing material 17 is performed atatmospheric pressure.

[0075] Next, as shown in FIG. 9, this substrate 10 is housed in adecompression chamber 18, the pressure inside the decompression chamber18 is reduced, and the substrate 10 is immersed in the plating solution20 stored in a plating solution bath 19 inside the decompression chamber18 while maintaining this state of reduced pressure (see FIG. 10). Here,a vacuum pressure on the order of 10⁻³ to 10⁻⁵ Pa for an aspect ratio ofthe through holes 11 of 0.1 to 200 is suitable for the reduced pressure.In FIGS. 9 and 10, reference symbol 19 a indicates heaters providedaround the plating solution bath 19. Immersion of the substrate 10 intothe plating solution 20 is carried out in a state in which thissubstrate 10 is maintained nearly horizontal by attaching a raising andlowering jig 21 installed within the decompression chamber 18 andlowering this raising and lowering jig 21.

[0076] Furthermore, the substrate 10 attached to the raising andlowering jig 21 is raised and lowered while maintained nearly horizontalby raising and lowering of the raising and lowering jig 21, and removalof this substrate 10 from the plating solution 20 is also carried outwhile maintaining the substrate 10 nearly horizontal.

[0077] The sealing material 17 is not limited to a heat-resistant film,but rather may be any material that is capable of sealing the openingsof the through holes 11 on the bottom surface 14 of the substrate 10,and its shape is also not limited to a constitution in which it coversthe entirety of the bottom surface 14 as with the previously mentionedheat-resistant film.

[0078] Here, although the plating solution 20 is specifically that whichhas resulted from the heating and melting of a gold-tin eutectic binder(Au-20 wt % Sn), the plating solution as claimed in the presentinvention is not limited to this, but rather a binder based on agold-tin alloy having a different composition, or a tin (Sn), indium(In) or other metal binder, as well as a tin-lead (Sn—Pb)-based, tin(Sn)-based, lead (Pb)-based, gold (Au)-based, indium (In)-based oraluminum (Al)-based binder can also be used. However, a combinationbetween the metal layer (and particularly the surface layer) and theplating solution should be selected so as to adequately ensurewettability between them.

[0079] Immersion of the substrate 10 into the plating solution 20 iscarried out with the bottom surface 14 to which the sealing material 17is affixed facing downward, and the top surface 13 facing upward, andthe entirety of the substrate 10 is submerged in the plating solution 20so that the top surface 13 is not exposed. However, at this stage,inflow of the plating solution 20 into the through holes 11, which arefine holes having a high aspect ratio and a diameter on the order ofseveral tens of micrometers that pass through the substrate 10 having athickness on the order of several hundred micrometers, has hardly begun.

[0080] Once immersion of the substrate 10 into the plating solution 20has been completed, the inside of the decompression chamber 18 ispressurized. As shown in FIG. 11A, prior to pressurization of the insideof the decompression chamber 18, since a state of reduced pressure inthe through holes 11 in which the plating solution 20 is has not flownis maintained by the plating solution 20 and sealing material 17 thatcover the openings (openings on the side of the top surface 13) of thethrough holes 11. Therefore, by pressuring the inside of thepressurization chamber 18, the plating solution 20 is able to reliablyflow into and fill the inside of the through holes 11 (see FIGS. 11B and12). The pressure during this pressurization should be equal to orgreater than atmospheric pressure. In addition, at this time, since thewettability of the plating solution 20 is ensured by the metal layer 15formed on the inner surface of the end portion of each through holes 11on the side of the bottom surface 14, the plating solution 20 acclimateswell with the inner surface of the through holes 11 even in the vicinityof the side of the bottom surface 14 of the through holes 11, and sinceit is filled without forming voids within the through holes 11, theplating solution 20 can be reliably filled throughout the through holes11.

[0081] Pressurization of the inside of the decompression chamber 18 canalso be carried out by feeding an inert gas such as nitrogen gas intothe decompression chamber 18, and in this case, incorporation of oxygeninto the plating solution prior to solidification can be prevented bythe inert gas atmosphere, thereby offering the advantage of preventingdeterioration of the properties of the plating solution on the substrate10 and inside the through holes 11.

[0082] (Cooling and Solidification Step)

[0083] Once filling of the plating solution 20 into the through holes 11is completed, as shown in FIG. 13, the substrate 10 is lifted out fromthe plating solution 20. At this time, since openings of the throughholes 11 on the side of the bottom surface 14 are maintained in a stateof being occluded by the heat-resistant film 17, the plating solution 20within the through holes 11 does not come out from the bottom surface14. In addition, there is also no occurrence of the problem of theplating solution 20 filled into the through holes 11 running out fromthe openings of the through holes 11 on the side of the top surface 13due to the wettability of the plating solution 20 with respect to themetal film 15 formed on the inner surface near the openings of thethrough holes 11 on the side of the top surface 13 and around thoseopenings.

[0084] The plating solution 20 along a metal pattern (made of the metalfilm 15) formed in the metallization step remains adhered on the topsurface 13 of the substrate 10 without falling off after the substrate10 has been lifted out from the plating solution 20. In areas other thanthe metal pattern, since the wettability of the plating solution 20-withrespect to the substrate 10 is poor, the plating solution 20 drops offaccompanying lifting of the substrate 10 from the plating solution 20.

[0085] For example, as shown in FIG. 7, in the case a circular metallayer 15 has been formed around the opening of each through holes 11corresponding to the shape of a bump, the plating solution 20 continuouswith the through holes 11 is padded at the areas where this metal layer15 and the opening of the through hole 11 are present (area where themetal layer 15 is present on the top surface 13 and area where theopening of the through hole 11 is present).

[0086] Once the substrate 10 is lifted out of the plating solution 20,the substrate 10 is cooled to solidify the plating solution 20 filledinto the through holes 11 as well as the above patted plating solution20. As a result, as shown in FIG. 14, through wirings 22 comprised bysolidifying the plating solution 20 in through holes 11, and bumps 23protruding from the top surface 13, are formed unitarily to obtain asubstrate with through wirings in which filled metal sections (throughwirings 22) and external metal sections (bumps 23) have been formed.

[0087] As was previously described, since outflow of the platingsolution 20 from the through holes 11 accompanying lifting out of thesubstrate 10 from the plating solution 20 is prevented, and the filledstate of the plating solution 20 in the through holes 11 can be reliablymaintained, the through wirings 22 are reliably obtained without defectssuch as internal voids. In addition, since the plating solution 20 is apeak shape at the areas where the metal layer 15 and openings of thethrough holes 11 are present due to its surface tension, as a result ofcooling and solidifying the plating solution 20, a peak-shaped bumps 23are formed protruding from the top surface 13.

[0088] In this manner, in a constitution in which the through wirings 22and bumps 23 are formed unitarily, there are no problems such asdefective bonding and electrical properties can be reliably ensured ascompared with constitutions in which the bumps are formed separatelyfrom through wirings and then bonded with through wirings. In addition,there is also no problem of brittleness of bonded sections (bondedsections between the bumps and through wirings) caused by differences incoefficients of thermal expansion or diffusion of materials as occurs inthe case of the bumps and through wirings being of different materials,thereby enabling long-term reliability to be improved.

[0089]FIG. 15 is a drawing of a comparative example in which metal layer15 is not formed on a substrate, namely only a plating solution fillingstep and cooling and solidification step are carried out withoutcarrying out a metallization step. In FIG. 15, a substrate 3 is the sameas the substrate 10 explained in the present embodiment, and the platingsolution indicated with reference symbol 2 in FIG. 15 is the same as theplating solution 20 explained in the present embodiment. In this case aswell, although a plating solution 2 has been filled into the entirety ofthrough holes 1 of the substrate 3 in the plating solution filling step,the plating solution flows out from the through holes 1 when thesubstrate 3 is lifted out from the plating solution in the platingsolution bath 19, and as a result, the plating solution 2 was confirmedto be insufficiently filled into the through holes 1, and a leveldifference D was confirmed to be formed in which the upper surface ofthe plating solution 2 was several micrometers to several tens ofmicrometers lower than a surface 4 of the substrate 3 that is the upperside when the substrate 3 is lifted out of the plating solution 2. Onthe basis of these results, it is clear that the through wiring formingmethod as claimed in the present invention demonstrates effects thatprevent the outflow of the plating solution by the metal layer 15 formedon the inner surface of the through holes in the vicinity of openingsand around the openings of the through holes in the top surface.

[0090] Furthermore, although the through wiring forming method asclaimed in the present invention has also been verified with respect tothe case of forming the metal layer only on the inner surface of throughholes in the vicinity of openings, but omitting the formation of themetal layer around the openings of the through holes in the top surfaceof the substrate, although it is difficult to form bumps of adequatesize, the outflow of the plating solution from the through holesaccompanying lifting of the substrate from the plating solution can beprevented, and there is no occurrence of problems such as the occurrenceof a level difference due to insufficient filling of the platingsolution. In this case, for example, effects are obtained such as beingable to reduce the occurrence of bonding defects to an extremely lowlevel when forming bumps to be bonded with through wirings in a separatestep.

Second Embodiment

[0091] Next, an explanation is provided of a second embodiment of thepresent invention.

[0092] In a metal filling method of this embodiment, a substrate(hereinafter, work piece may be referred to as a “substrate”) in whichnon-through holes 51 (fine holes) are formed is employed as a work piece50 a, and filled metal sections and bumps are formed by filling theplating solution into the non-through holes 51 and solidifying theplating solution.

[0093] As shown in FIG. 16, in the present embodiment, a glass substratein which a plurality of fine holes in the form of non-through holes 51are formed, is used as an example of a constitution of the substrate 50,however, the constitution other than the non-through holes 51 of thesubstrate 50 (such as the material) can be the same as that of thesubstrate 10 of the first embodiment.

[0094] The non-through holes 51 formed in the substrate 50 function asinner via holes and so forth. The inner diameter of these non-throughholes 51 may be the same as the through holes 11 (fine holes) of thesubstrate 10 of the first embodiment. All of the non-through holes 51formed in substrate 50 are open only on one side of the substrate 50(here, a top surface 53), and are formed so as to be extending towards abottom surface 54 of the substrate 50 in nearly a straight line from theopenings in the top surface 53.

[0095] In this metal filling method, a metallization step, a platingsolution filling step, and a cooling and solidification step are carriedout using the substrate 50 in the same order as the first embodiment.However, since the fine holes 51 of the substrate 50 used in this metalfilling method are non-through holes, only one end along the axialdirection is open in the outer surface of the substrate 50 (here, thetop surface 53), and the other end in the axial direction is occluded,it is not necessary to use a sealing material when removing (and morespecifically, lifting out) the substrate 50 from the plating solution 20after having been immersed in the plating solution 20 in the platingsolution filling step. With the exception affixing and removing thesealing material from the substrate 50, a constitution is employed inwhich the metallization step, plating solution filling step and coolingand solidification step are carried out in the same manner as the firstembodiment. In addition, the plasma pre-treatment step and so forth arealso carried out in the same manner as the first embodiment.

[0096] Moreover, in the metal filling method explained here, a filledmetal section exposure step (to be described later), in which filledmetal sections are exposed on the substrate bottom surface is exposed,is added after the cooling and solidification step.

[0097]FIG. 17 is a drawing showing the substrate 50 on which ametallization-step has been completed, wherein reference symbol 52indicates an electrical insulating layer such as an oxide film, andreference symbol 55 indicates a metal layer. Although the metal layer 55is formed on the inner surface of the fine holes 51 and around theopenings of the fine holes 51 in the top surface 53 of the work piece50, similar to the metal layer in the first embodiment, the range overwhich it is formed on the inner surface of the fine holes 51 is inwardto a location at least several tens of micrometers from the openings ofthe fine holes 51 towards the bottom of the fine holes 51.

[0098]FIG. 18 is a drawing showing the state in which the substrate 50is immersed in the plating solution in the metal filling step, and showsthe state in which the substrate 50 is immersed in the plating solution20 within the plating solution bath 19 installed within thedecompression chamber 18. Although this metal filling step is the sameas that of the first embodiment, the use of a sealing material can beomitted as shown in the drawing.

[0099]FIG. 19 shows the state in which filled metal sections 56 areunitarily formed with external metal sections 57 (e.g., bumps) bycooling the substrate 50 after having been removed from the platingsolution 20, and then solidifying the plating solution 20 filled insidethe fine holes 51 as well as the plating solution 20 that has beenpadded so as to protrude from the substrate 50 in the vicinity of theopenings of the fine holes 51 in a cooling and solidification step. Thesubstrate 50 shown in FIG. 19, namely, the substrate 50 on which thefilled metal sections 56 and external metal sections 57 have beenformed, corresponds to a member with filled metal sections as claimed inthe present invention.

[0100]FIG. 20 is a drawing showing the above filled metal sectionexposure step, and shows the state in which the bottom surface of thesubstrate 50 following completion of the cooling and solidification stepis polished to expose the filled metal sections 56 in the fine holes 51.As a result, the filled metal sections 56 are able to function asthrough wirings and so forth of the substrate 50. The substrate shown inFIG. 20 also corresponds to a member with filled metal sections asclaimed in the present inventiont.

[0101] Various techniques can be employed for exposing filled the metalsections 56 on the bottom surface of the substrate 50, examples of whichinclude partial removal of the substrate 50 by wet etching in additionto the polishing method mentioned above.

Third Embodiment

[0102] The following provides an explanation of a third embodiment ofthe present invention.

[0103]FIG. 21 shows an example of forming a filled metal section 26 andexternal metal section 27 by employing a work piece in the form ofrod-shaped member 24 (hereinafter, work piece may be referred to as the“rod-shaped member”) and filling plating solution in the form of tininto a through hole 25 having a diameter of 0.1 mm and total length of 5mm provided along the axial direction of this rod-shaped member(vertical direction in FIG. 21) using the same technique as the firstembodiment (by sequentially carrying out a metallization step, platingsolution filling step and cooling and solidification step in the samemanner as previously described, wherein a side 28 of the upper surfaceof this work piece 24 to be described later corresponds to the substratetop surface, and the opposite side corresponds to the substrate bottomsurface). Various types of technique can be employed for forming throughholes in the work piece 24, an example of which is the previouslymentioned DRIE method.

[0104] Although a glass rod is used here for the work piece 24(rod-shaped member), the work piece is not limited to this, but ratherthat formed from one type of material selected from ceramic, silicon andvarious types of synthetic resins, or that formed from a compoundmaterial comprised of two or more materials selected from glass,ceramic, silicon and various types of synthetic resins, can also beused. The type and forming method of the metal layer 15, theheat-resistant film 17 and so forth that are employed are the same asthose previously described. However, the range over which the metallayer 15 is formed is the range equal to roughly 2 to 3 times thediameter of the through hole 25 from both ends in the axial direction ofthe through hole 25 towards the center in the axial direction, androughly several millimeters from the outer circumference of the openingaround said opening of the through hole 25 on both opposing sides in theaxial direction of the rod-shaped member 24.

[0105] Although the technique for filling the plating solution into thethrough hole 25 is the same as the plating solution filling steppreviously described, immersion and removal of the rod-shaped member 24with respect to the plating solution stored in the plating solution bath19 inside the decompression chamber 18 is performed with the side onwhich the heat-resistant film 17 is provided facing downward. Inexplaining this with reference to FIG. 22 (FIG. 22 shows the state inwhich the work piece 24 has been lifted out from the plating solution20), the work piece 24, following completion of formation of the metallayer 15, is attached to the raising and lowering jig 21 inside thedecompression chamber 18, and is raised and lowered within thedecompression chamber 18 while maintaining the orientation in which thethrough hole 25 is vertical by raising and lowering of the raising andlowering jig 21. However, the opening of the other end in the axialdirection facing downward in opposition to one end in the axialdirection of the through hole 25 facing upward when housed in thedecompression chamber 18 is covered in advance with the sealing material17 prior to being housed in the decompression chamber 18. Once this workpiece 24 has been housed in the decompression chamber 18, the pressureinside the decompression chamber 18 is reduced, the work piece 24 islowered while maintaining this reduced pressure state, and immersed inthe plating solution 20 stored within the plating solution bath 19inside the decompression chamber 18. Next, with the work piece 24 stillimmersed in the plating solution 20, the inside of the decompressionchamber 18 is pressurized causing the plating solution 20 to be filledinto the through hole 25. Next, the work piece 24 is raised up, liftedout from the plating solution 20 and cooled.

[0106] In this example as well, similar to the case of the previouslydescribed substrate 10, filling of the plating solution throughout thethrough hole 25 can be carried out reliably. In addition, the platingsolution continuous with the through hole 25 is padded on the opening ofthe through hole 25 on the surface 28 of the upper side of the workpiece 24 that has been removed (and more specifically, lifted out) fromthe plating solution 20 (the side of the work piece 24 in which one endof the through hole 25 is open) and where the metal layer 15 is presentaround the opening. Therefore, the filled metal section 26, which iscomprised by cooling the work piece 24 that has been lifted out from theplating solution 20 followed by solidifying the plating solution 20within the through hole 25, and the external metal section 27, which iscomprised by solidification of the above padded plating solution 20, canbe formed unitarily, thereby obtaining a member with filled metalsections having the filled metal sections 26 and external metal sections27.

[0107] Here, the solid filled metal sections 26 free of voids can beformed within the resulting member with filled metal sections. Inaddition, although the diameter (inner diameter) of the through hole 25is larger than that of the through holes 11 of the substrate 10previously described, since the filled metal section 26 is such that thethrough hole 25 is filled throughout, including one end in the axialdirection of the through hole 25, and a level difference is not formedon one end in the axial direction of the through hole 25 such that theend of the filled metal section 26 drops in from the side of the workpiece 24, outflow of the plating solution from the through hole 25 whenthe rod-shaped member 24 is lifted out from the plating solution bath 19is considered to be prevented in this example as well.

Fourth Embodiment

[0108] The following provides an explanation of a fourth embodiment ofthe present invention.

[0109] Although this embodiment is the same as the third embodiment withrespect to the use of a similar rod-shaped member for a work piece 30(hereinafter, the work piece may be referred to as a rod-shaped member),as shown in FIG. 11, it differs with respect to a fine hole 31 formedbeing a non-through hole in which only one end along the axial directionof a rod-shaped member is open, while the other end in the axialdirection is not open (hereinafter, the fine hole may be referred to asa non-through hole).

[0110] In the metal filling method of this embodiment as well, althougha metallization step, plating solution filling step and cooling andsolidification step are sequentially carried out in the same manner asthe third embodiment, since the fine hole 31 formed in the work piece 30is a non-through hole, there is no need to use a sealing material.

[0111]FIG. 23 shows the work piece 30 on which a cooling andsolidification step has been completed. As shown in FIG. 23, the workpiece 30 on which the filled metal section 26 and external metal section27 have been formed is a member with metal filled sections as claimed inthis embodiment. In addition, in the metal filling method of thisembodiment, the filled metal section 26 can also be exposed on the otherend in the axial direction of the rod-shaped member 30 by adding afilled metal section exposure step following the cooling andsolidification step. In other words, by removing the portion below avirtual line 32 in FIG. 23 of the member with metal filled sections (orthe work piece 30) shown in FIG. 23 by polishing and so forth, the metalfilled section 26 can be used as a through wiring and so forth since themetal filled section 26 is exposed.

[0112] Furthermore, the present invention is not limited to theabove-mentioned embodiments, but rather can be altered to achievevarious variations.

[0113] For example, the technique used to form the metal layer is notlimited to the above-mentioned sputtering, but rather plating (byimmersing the substrate in plating liquid) and so forth can also beemployed.

[0114] Although a substrate and rod-shaped member were indicated asexamples of a work piece in the above embodiments with respect to themetal filling method as claimed in the present invention, the presentinvention is not limited to these, but rather various types of shapes,materials and so forth can be used for the specific shape, material andso forth of the work piece.

[0115] Immersion of the substrate or work piece into the platingsolution and removal from the plating solution are not limited to beingcarried out in an orientation in which the side on which through holesare occluded by a sealing material in the form of a heat-resistant filmis facing downward as was exemplified in the drawings in so forth, butrather a large degree of freedom is able to be secured for theorientation during immersion of the work piece in the plating solutionand removal (lifting out) of the work piece from the plating solutiondepending on, for example, the wettability between the metal layerformed on the inner surface in the vicinity of openings of through holesand the plating solution that has flowed into the through holes, thefluidity of the plating solution and other conditions.

1. A metal filling method comprising: a first step of forming a finehole in a work piece: a second step of forming a metal layer on an innersurface of one end of said fine hole and a third step of filling amolten metal into said fine hole;
 2. A metal filling method according toclaim 1, wherein: said fine hole is a through hole that passes extendsthrough said work piece; in said second step, said metal layer is formedon the inner surface of at least one end of both ends in an axialdirection of said through hole: in said third step, by immersing saidwork piece, into said molten metal, said molten metal is filled intosaid through hole and the metal filling method further-comprises afourth step of closing at least one of two openings of said throughhole, and a fifth step of removing said work piece out from said moltenmetal
 3. A metal filling method according to claim 2, wherein: in saidsecond step, said metal layer is further formed on the surface of saidwork piece and around the opening in said one end in said fifth step, apadding portion which is united with said molten metal filled into saidfine hole is formed on said outer surface by removing said work pieceout from said molten metal; and the metal filling method furthercomprises a sixth step of solidifying said molten metal within said finehole and said molten metal forming said padding portion.
 4. A metalfilling method according to claim
 1. wherein: said work piece is asubstrate: and said fine hole is formed as a non-through hole whichopens to only one of top and bottom surfaces of said substrate
 5. Ametal filling method according to claim 3, wherein, a shape of saidmetal layer formed on the outer surface of said work piece is patternedcorresponding to a shape of said padding portion to be formed. 6.(Cancelled)
 7. (Cancelled)
 8. A metal filling method according to claim1, wherein: said work piece is a substrate; and said fine hole is formedas a through hole, which opens to both top and bottom surfaces of saidsubstrate.